The present invention relates to a well completion system and method for recovering production fluid, such as oil, from an oil or gas well, and, more particularly, to such a system and method utilizing reeled tubing for controlling the flow of the production fluid from the well.
In the operation of subterranean oil and gas earth wells, various types of equipment have evolved for controlling the flow of production fluid to the ground surface. This equipment is usually connected in, or to, a string of production tubing formed by a plurality of tubing sections.
Reeled tubing i.e. continuous, relatively thin-walled, bendable tubing, is becoming more and more popular in downhole servicing of oil and gas wells since it has many advantages when compared to wireline or connected tubing sections. For example, reeled tubing can be more rapidly inserted into the well and can be more easily passed through downhole equipment. Also, the reeled tubing can traverse highly deviated, or horizontal, wells which could otherwise not be traversed with wireline or threaded tubing in a controlled manner.
Although reeled tubing would be ideally suited for well completion systems since it would enjoy the above advantages and, in addition, eliminate the multiple joints between the production tubing sections, reeled tubing has not enjoyed widespread use in this manner for several reasons. For example, its relatively thin walls preclude threading for attaching the tubing to completion equipment such as pumps, landing nipples, safety values, well hangers, etc. Also, there has been no known effective use of reeled tubing for conveying production fluid from the formation to ground surface due to the need for relatively sophisticated high pressure sealing and blow-out prevention techniques. Further, many connections of the various components making up a well completion system require relative rotation between the various components. For example, when a section of tubing is attached to a well completion tool, matching threads are formed on the tool and the tubing, or to a sub attached to the tubing, so that the connection can be made by advancing and rotating one of the components relative to the other. However, these type of connections have stress limitations that are well below the stress limitations of a continuous section of reeled tubing. Also, these type of connections are inadequate when the reeled tubing is connected to downhole tools having a rotary component such as electrical submersible well pumps which are often used in well completion systems to pump production fluid from a formation, into and through a casing string and a production tubing string, and to a wellhead above surface.
Another reason that reeled tubing has not enjoyed widespread use in well completion systems is that emergency release devices are often used to connect the reeled tubing to certain operating tools for providing a quick and reliable disconnect during emergency conditions, such as, for example, when the operating tool is jammed in the well. (An emergency release device of this type is disclosed in U.S. Pat. No. 4,986,362 assigned to the assignee of the present invention.) However, if reeled tubing is used in a well completion environment with tools having a rotary component, the emergency release device discussed above does not lock against rotation of the operating tool relative to the reeled tubing. Therefore, if the rotating component of the tool becomes jammed, one component of the emergency release device would rotate, or free-wheel, relative to the other. This makes it difficult to free the jammed rotary tool.
Another potential disadvantage of reeled tubing in this context is that, in well completion systems a safety valve is usually deployed in the well completion string for blocking the flow of production fluid to the ground surface under emergency conditions. However, if reeled tubing is used in the string and the safety valve is activated to shut off, reactive forces are created which would tend to bend the reeled tubing and cause leakage of the production fluid.